The present invention generally relates to cellular and wireless communication, and more particularly to a cellular system that multiplexes real time users with non-real time users on a shared packet data traffic channel. A mobile station user engaged in real time traffic can back off during in-active periods and enable mobile station users engaged in non-real time traffic to access the channel. A fast Notification Access Channel (NACH) enables the real time user to take the channel back with minimum delay as soon as it is needed.
Recently, there has been a trend in the telecommunication community to focus more and more on wireless packet data communication rather than circuit switched communication. With the tremendous increase of Internet users, and usage of Internet protocols, it is believed that the packet switched communication will soon become larger than the circuit switched communication that today dominates, e.g., the cellular communication. Cellular communication system manufacturers and operators are therefore looking for solutions to integrate their circuit switched services with wireless packet switched services that can provide reliable and more spectrum efficient connections for packet switched users, e.g., Internet users. This trend has made different types of packet switched communication system evolutions flourish. One of the more well known packet switched cellular systems in the telecommunications community is the extension of the present GSM (Global System for Mobile Communications) cellular communication system, called GPRS (General Packet Radio Service).
GPRS is a packet switched system that uses the same physical carrier structure as the present GSM cellular communication system and is designed to coexist and provide the same coverage as GSM. GPRS radio interface is thus based on a TDMA (Time Division Multiple Access) structured system with 200 kHz carriers divided into eight timeslots with GMSK (Gaussian Minimum Shift Keying) modulation. The multiplexing is such that several users can be allocated on the same timeslot, and use it only when data needs to be transmitted. One user can also be allocated more than one timeslot to increase its throughput of data over the air.
The GPRS specification includes a number of different coding schemes to be used dependent on the quality of the radio carrier. With GPRS, data rates well over 100 kbps will be possible.
There is also ongoing a development and standardization of a new air interface mode in GSM, which will affect both packet and circuit switched modes. This new air interface mode is called EDGE, Enhanced Data rates for Global Evolution. EDGE""s main features are new modulation and coding schemes for both packet switched and circuit switched data communication. In addition to the Gaussian Minimum Shift Keying (GMSK) modulation, which today is used in both GPRS and GSM circuit switched mode, an 8 symbol Phase Shift Keying (8PSK) modulation is introduced. This modulation can provide users with higher data rates than GMSK in good radio environments.
The packet data mode with EDGE modulation is called EGPRS (Enhanced GPRS) and the circuit switched data mode is called ECSD, Enhanced Circuit Switched Data. With EGPRS, data rates over 384 kbps will be possible with EDGE.
Recent development for another TDMA based cellular system, the cellular communication system compliant to the ANSI/136 standard, below referred to as TDMA/136 has been focused on a packet data system to be integrated with the TDMA/136 circuit switched mode.
This packet data system will also be based on the new EDGE technology as defined for the GPRS extension. It will then allow TDMA/136 operators with a packet data mode to provide data rates up to 384 kbps on 200 kHz carriers with GMSK and 8PSK modulation as defined for EGPRS.
Two modes of EGPRS will be standardized for use together with TDMA/136 systems, one which relies on time synchronization between base stations in the system and one which does not. These two modes are generally referred to as COMPACT and Classic respectively.
While the evolution of cellular packet data communication initially has focused on developing a system that efficiently utilize resources to transfer delay-insensitive data, the focus is now shifting towards delay sensitive transmissions and higher quality of service requirements.
A cellular packet data capable mobile station may set up a packet data session in order to send and receive packet data. The mobile station may connect to an Internet server providing packet data service. The connection over the Internet can utilize the TCP/IP protocol for end-to-end delivery. The mobile station can access the fixed network via a packet data channel over the air-interface.
The packet data channel is a shared resource, such that several users can be statistically multiplexed on the channel. This is quite different from traditional cellular circuit switched channels, where each user has exclusive access to a channel regardless of whether or not it is actually being used to send or receive data. When the mobile station is engaged in real time traffic the associated data transmission is very much delay sensitive. This is why a circuit switched channel is good for voice applications, where a user is allocated exclusive use of a traffic channel, where it can transmit and receive speech frames. When the user starts to talk the quality of service perceived will in part be based upon the presence of delay and as such the transmission of speech related data should be delayed as little as possible. On the shared packet data channel, on the other hand, a real time user can perceive a problem in the form of a noticeable delay, if another user already occupies the channel when the real time user starts to talk. The real time user must therefore quickly get access to the packet data channel in order to minimize the delay in the transmission of the speech frames.
There are basically two known methods available for a mobile station to gain access to a shared packet data channel when it is currently not allocated ownership of the resources supported thereon. To do so it must make the base station, that is the resource allocation arbitrator, aware of the mobile station""s need to transmit on the shared channel. The first method is for the mobile station to wait until it is allocated time to transmit by the base station. This will eventually occur since the base station is aware that the mobile station is present but temporarily has no allocated resources because of multiplexing in another user. The problem with the first method is that it might take considerable time until the base station allocates channel resources to the mobile station supporting a real time user. There is no way for the base station to know the real time needs of all the mobile stations that are currently sharing the packet data channel.
The second method is based on the mobile station sending a random access message on the random access channel in order to notify the base station that the mobile station needs to transmit and that the base station should therefore immediately allocate radio resources to the requesting mobile station. For the second method, the random access channel is shared by an indefinite number of mobile stations on a contention basis. The random access channel is subject to collisions and there is therefore no guarantee as to the extent of the delay experienced prior to receiving allocation of resources on the channel. Since it might take considerable time before the resource allocation request message gets through to the base station this could result in a very noticeable impact on the quality of service perceived by the real time user.
From the moment the mobile station determines it has data to transmit until the time the mobile station has acquired resource ownership on the packet data channel, no data can be sent to or received from the mobile station. For a mobile station user running a real time application this delay may result in a perceivable degradation of service quality. In the interest of enhancing the quality of service provided to users, it is therefore important to minimize this delay experienced by a mobile station as it moves from active mode with no resources allocated to active mode with resources allocated.
The present invention is directed to solving one or more of the problems discussed above.
In accordance with the invention, a fast notification channel minimizes delay for real time users to be allocated resources in a shared cellular packet data system.
Broadly, there is disclosed herein the method of multiplexing users on a shared cellular packet data traffic channel. The method comprises the steps of transmitting packet data by a first select mobile station on the shared packet data traffic channel to a base station until a transmit queue is empty; the base station thereafter allocating uplink on the shared packet data channel to a second select mobile station, the first select mobile station upon having data to transmit in its transmit queue transmitting a notification signal to the base station, the notification signal uniquely identifying the first select mobile station on the shared cellular packet data traffic channel; and the base station, after receiving the notification signal, allocating uplink on the shared packet data channel to the first select mobile station.
It is a feature of the inventive method to further provide the step of setting up a packet data session prior to the first select mobile station transmitting packet data and wherein the notification signal is assigned by the base station to the first select mobile station during setting up of the packet data session. The step of setting up the packet data session comprises assigning a select frequency to the first select mobile station by the base station, and wherein the step of transmitting the notification signal by the first select mobile station comprises transmitting a tone signal at the select frequency.
It is another feature of the invention to further provide the step of providing a notification access channel and wherein the notification signal is transmitted by the first select mobile station on the notification access channel. The step of providing the notification access channel comprises assigning select time slots of a packet random access channel to the notification access channel. The notification access channel is periodically monitored the by the base station to detect the notification signal.
It is still another feature of the invention that the step of providing a notification access channel comprises providing plural tone frequencies to be assigned to plural mobile stations transmitting packet data on the shared packet data channel. The notification access channel is periodically monitored by the base station to detect the notification signal comprising one of the plural tone frequencies. The base station is operable to detect plural tone frequencies simultaneously on the notification access channel.
There is disclosed in accordance with another aspect of the invention the method of obtaining quick access to a shared cellular packet data traffic channel. The method comprises the steps of providing a notification access channel for mobile stations engaged in packet data sessions on the shared packet data channel to request uplink from a base station; a select mobile station, upon having packet data to transmit, transmitting a notification signal to the base station on the notification access channel, the notification signal uniquely identifying the first mobile station on the shared cellular packet data traffic channel; and the base station, after receiving the notification signal, allocating uplink on the shared packet data channel to the select mobile station.
It is a feature of the invention of the inventive method to further provide the step of setting up a packet data session prior to the select mobile station transmitting packet data and wherein the notification signal is assigned by the base station to the select mobile station during setting up of the packet data session. The step of setting up the packet data session comprises assigning a select frequency to the select mobile station by the base station, and wherein the step of transmitting the notification signal by the select mobile station comprises transmitting a tone signal at the select frequency
It is another feature of the invention that the step of providing the notification access channel comprises assigning select time slots of a packet random access channel to the notification access channel.
It is still another feature of the invention to provide the step of periodically monitoring the notification access channel by the base station to detect the notification signal.
There is disclosed in accordance with a further aspect of the invention, a system for multiplexing users on a shared cellular packet data traffic channel in a cellular packet data network system. The system includes a mobile station having a mobile station control system. The mobile station control system transmits packet data on the shared packet data traffic channel to a base station until it reaches an inactive period, and upon having additional data to transmit, transmits a notification signal to the base station, the notification signal uniquely identifying the mobile station on the shared cellular packet data traffic channel. A network control system is operatively associated with the base station. The network control system allocates uplink on the shared packet data channel to the mobile station after receiving the notification signal until the mobile station reaches the inactive period.
It is a feature of the invention that the notification signal is assigned by the network control system to the mobile station during setting up of a packet data session. The network control system assigns a select frequency to the mobile station. The mobile station control system transmits the notification signal by transmitting a tone signal at the select frequency.
It is another feature of the invention to provide a notification access channel comprising select time slots of a packet random access channel. The mobile station transmits the notification signal on the notification access channel. The network control system periodically monitors the notification access channel to detect the notification signal. The network control system assigns unique tone frequencies, representing the notification signal, to plural mobile stations transmitting packet data on the shared packet data channel. The network control system is operable to detect plural tone frequencies simultaneously on the notification access channel.
Further features and advantages of the invention will be readily apparent from the specification and the drawings.